1. Field of the Invention
This invention relates to a method of manufacturing a waveguide circuit element with a low energy-loss suitable for use in ultrashort wave bands.
2. Description of the Prior Art
It is generally required to minimize the electric loss on the internal surface of a recessed portion of a waveguide circuit element for ultrashort wave band along which electric waves are transmitted.
In order to achieve this purpose, the accuracy with which the internal surface of the recessed portion is made up is of primary importance in the manufacture of the waveguide circuit element. In this connection, the dimensional error of the internal surface of the recessed portion is required to be maintained not more than several microns and also the internal surface of the recessed portion should be mirror-finished in such a manner that the difference in height between the highest and lowest portions of the surface excepting an abnormally high or low portion is not more than 0.2 .mu.m. Further, it is desirable that a metal layer constituting the internal surface should be low in resistivity as far as possible.
In the conventional method of manufacturing a waveguide circuit element such as a cavity resonator, a base metal of copper, brass or phosphorus bronze is hollowed out on a machine such as a lathe to form a recess and then the internal surface of the recessed portion is plated with a metal with a low resistivity. As an alternative, a male die adapted to fit a desired recess is made of aluminum or stainless steel and a copper electro-forming is effected on it, followed by the removal of the male die and the electroplating of a metal with a low resistivity on the internal surface of the recessed portion.
The conventional methods described above have the following disadvantages:
1. The portion of the base metal where the electroplating is effected is the internal surface of the base metal and therefore it is often difficult to finish that portion uniformly. PA1 2. The manufacturing processes are complicated. For these reasons, the accuracy in dimension and shape of the recess as well as the fineness of the surface thereof is reduced, and also a high resistivity of the surface of the recessed portion results, making it difficult to obtain a low energy-loss cavity resonator.